Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 01 :: Mechanical Engineering

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Q1. If the flow of air through the compressor is perpendicular to its axis, then it is a

(A) Reciprocating compressor
(B) Centrifugal compressor
(C) Axial flow compressor
(D) Turbo compressor

Answer: (B) Centrifugal compressor


Q2. To avoid moisture troubles, the branch connections from compressed air lines should be taken from

(A) Top side of main
(B) Bottom side of main
(C) Left side of main
(D) Right side of main

Answer: (A) Top side of main


Q3. Separators in compressor installations are located

(A) Before inter-cooler
(B) After inter-cooler
(C) After receiver
(D) Between after-cooler and air receiver

Answer: (D) Between after-cooler and air receiver


Q4. A rotary compressor is driven by an

(A) Electric motor
(B) Engine
(C) Either (A) or (B)
(D) None of these

Answer: (C) Either (A) or (B)


Q5. In a turbo jet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded in

(A) Exit nozzle, which is a constant volume process
(B) Exit nozzle, which is essentially an isentropic process
(C) Turbine blades, which is a constant volume process
(D) Turbine blades, which is essentially an isentropic process

Answer: (D) Turbine blades, which is essentially an isentropic process


Q6. The capacity of a compressor is expressed in

(A) kg/m²
(B) kg/m³
(C) m³/min
(D) m³/kg

Answer: (C) m³/min


Q7. Rotary compressor is best suited for

(A) Large quantity of air at high pressure
(B) Small quantity of air at high pressure
(C) Small quantity of air at low pressure
(D) Large quantity of air at low pressure

Answer: (B) Small quantity of air at high pressure


Q8. Rotary compressors are used for delivering

(A) Small quantities of air at high pressures
(B) Large quantities of air at high pressures
(C) Small quantities of air at low pressures
(D) Large quantities of air at low pressures

Answer: (D) Large quantities of air at low pressures


Q9. In n₁ and n₂ are the indices of compression for the first and second stage of compression, then the ratio of work-done on the first and second stages (W₁/W₂) with perfect intercooling is given by

(A) W₁/W₂ = n₂(n₁ – 1)/n₁(n₂ – 1)
(B) W₁/W₂ = n₁(n₂ – 1)/n₂(n₁ – 1)
(C) W₁/W₂ = n₁/n₂
(D) W₁/W₂ = n₂/n₁

Answer: (B) W₁/W₂ = n₁(n₂ – 1)/n₂(n₁ – 1)


Q10. With the decrease in compression ratio, the volumetric efficiency

(A) Does not change
(B) Increases
(C) Decreases
(D) First decrease and then increase

Answer: (B) Increases


Q11. Gas turbines use following type of air compressor

(A) Centrifugal type
(B) Reciprocating type
(C) Lobe type
(D) Axial flow type

Answer: (D) Axial flow type


Q12. In an axial flow compressor, the ratio of pressure in the rotor blades to the pressure rise in the compressor in one stage is known as

(A) Work factor
(B) Slip factor
(C) Degree of reaction
(D) Pressure coefficient

Answer: (C) Degree of reaction


Q13. Pick up the wrong statement

(A) Pulse-jet requires no ambient air for propulsion
(B) Ramjet engine has no turbine
(C) Turbine drives compressor in a Turbojet
(D) Bypass turbojet engine increases the thrust without adversely affecting, the propulsive efficiency and fuel economy

Answer: (A) Pulse-jet requires no ambient air for propulsion


Q14. Isothermal compression though most efficient, but is not practicable because

(A) It requires very big cylinder
(B) It does not increase pressure much
(C) It is impossible in practice
(D) Compressor has to run at very slow speed to achieve it

Answer: (D) Compressor has to run at very slow speed to achieve it


Q15. 1 m of air at atmospheric condition weighs approximately

(A) 0.5 kg
(B) 1.0 kg
(C) 1.3 kg
(D) 2.2 kg

Answer: (C) 1.3 kg


Q16. The work done per unit mass of air in compression will be least when ‘n’ is equal to

(A) 1
(B) 1.2
(C) 1.3
(D) 1.4

Answer: (A) 1


Q17. The inter-cooler pressure, for minimum work required, for a two stage reciprocating air compressor, is given by (where p₁ = Intake pressure of air, p₂ = Inter-cooler pressure, and p₃ = Delivery pressure of air)

(A) p₂ = p₁ × p₃
(B) p₂ = p₁/p₃
(C) p₂ = p₁ × p₂
(D) p₂ = p₃/p₁

Answer: (C) p₂ = p₁ × p₂


Q18. More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than

(A) 2 kg/cm²
(B) 6 kg/cm²
(C) 10 kg/cm²
(D) 14.7 kg/cm²

Answer: (A) 2 kg/cm²


Q19. For supplying intermittent small quantity of air at high pressure, following compressor is best suited

(A) Centrifugal
(B) Reciprocating
(C) Axial
(D) Screw

Answer: (B) Reciprocating


Q20. Pick up wrong statement. Surging phenomenon in centrifugal compressor depends on

(A) Mass flow rate
(B) Pressure ratio
(C) Change in load
(D) Stagnation pressure at the outlet

Answer: (D) Stagnation pressure at the outlet


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